The authors describe an occult metastatic deposit in the kidney of a 22-year-old woman; such lesions are not usually detected until autopsy. They postulate that after the development of acute subcapsular hematoma, a "renal compartmental syndrome" occurred, leading to renal artery thrombosis. Primary vascular involvement by the metastatic osteosarcoma, which was remote from the renal hilus, was not identified pathologically.